Paper-based chemical assay devices include a paper substrate, wax that forms fluid channels and other fluid structures in the paper, and one or more reagents. Common examples of paper-based chemical assay devices include biomedical testing devices that are made of paper and perform biochemical assays and diagnostics in test fluids such as blood, urine and saliva. The devices are small, lightweight and low cost and have potential applications as diagnostic devices in healthcare, military and homeland security to mention a few. The current state of the art paper diagnostic device is limited on fluidic feature resolution and manufacturing compatibility due to uncontrolled reflow of the wax channel after the wax is printed on the paper.
FIG. 7A and FIG. 7B depict the prior art processes for melting wax that is formed on a paper substrate in a reflow oven. The melting process is required for the wax to penetrate into the paper instead of remaining in a layer on the surface of the paper. In FIG. 7A, a reflow oven heats a paper substrate with solidified wax to a temperature of approximately 150° C. The entire paper and the wax are heated to the same temperature in an isotropic manner. As depicted in FIG. 7B, the wax melts and spreads both into the porous paper and across the surface of the paper in a roughly uniform manner. The prior art reflow ovens can be used for low-volume production of biomedical devices. The wax melts and penetrates into the paper over the course of one or more minutes while the reflow oven holds the paper.
Prior art reflow ovens such as the oven of FIG. 7A are not suitable for use in large-scale production of biomedical devices and other devices that include structures that are formed within paper substrates. For example, in one embodiment a cut-sheet inkjet printer forms printed pattern of wax or another suitable hydrophobic material on a single sheet of paper, and the reflow oven in FIG. 7A heats the sheet of paper for two minutes to enable the wax to penetrate the paper. However, mass-production of a large number of the biomedical devices in an efficient manner requires the use of large scale inkjet printing systems that form printed patterns on large rolls of paper or other suitable substrates. The prior art reflow ovens are impractical for mass production of the biomedical devices with large scale printing systems. Consequently, improved methods and systems for the production of biomedical devices that do not require the prior art reflow ovens would be beneficial.